Time Step Expansions and the Invariant Manifold Approach to Lattice Boltzmann Models

Abstract

Summary. The classical method for deriving the macroscopic dynamics of a lattice Boltzmann system is to use a combination of different approximations and expansions. Usually a Chapman-Enskog analysis is performed, either on the continuous Boltzmann system, or its discrete velocity counterpart. Separately a discrete time approximation is introduced to the discrete velocity Boltzmann system, to achieve a practically useful approximation to the continuous system, for use in computation. Thereafter, with some additional arguments, the dynamics of the Chapman-Enskog expansion are linked to the discrete time system to produce the dynamics of the completely discrete scheme.In this paper we put forward a different route to the macroscopic dynamics. We begin with the system discrete in both velocity space and time. We hypothesize that the alternating steps of advection and relaxation, common to all lattice Boltzmann schemes, give rise to a slow invariant manifold. We perform a time step expansion of the discrete time dynamics using the invariance of the manifold. Finally we calculate the dynamics arising from this system.By choosing the fully discrete scheme as a starting point we avoid mixing approximations and arrive at a general form of the microscopic dynamics up to the second order in the time step. We calculate the macroscopic dynamics of two commonly used lattice schemes up to the first order, and hence find the precise form of the deviation from the Navier-Stokes equations in the dissipative term, arising from the discretization of velocity space.Finally we perform a short wave perturbation on the dynamics of these example systems, to find the necessary conditions for their stability.

Enhancement of the stability of lattice Boltzmann methods by dissipation control

“…All of the dissipation in the discrete system then occurs due to the relaxation operation. This dissipation occurs at different orders of the small parameter, the time step [28]. The first order gives an approximation to the Navier Stokes equations (with some error terms due to the discrete velocity system).…”